[BUG] Training/train-new-model page opens with an error

[ruudel]

Environment
https://admin.rit-test.buerokratt.ee/

Bug description:
When opening training/train-new-model there will pop up a repeating error:

The response is:
{"response":"Can't find trained model record."}

Expected behavior:
The page should open without issues.

[ahmer-mt]

@PaulaMerle There is logic in /training/GET/rasa/training/trained.ymlthat if there are no models with READY state then 409 is returned.